1. Field of the Invention
The present invention relates to a battery charging circuit, a portable electronic device and a semiconductor integrated circuit, which are capable of charging a battery.
2. Description of the Related Art
In portable electronic devices such as cellular telephones, personal handyphone system (PHS) terminals, personal digital assistances (PDAs) and personal computers (PCs), secondary batteries such as chargeable lithium batteries having excellent discharge characteristics are frequently used.
A battery charging circuit for charging a battery having a charging ON/OFF circuit and a backflow prevention circuit has been proposed (For example, refer to Japanese Patent Application Laid-open Publication No. 2001-119867). The charging ON/OFF circuit supplies power from a power source to the battery. The backflow prevention circuit prevents a battery from being discharged. Here, the backflow prevention circuit is connected between the charging ON/OFF circuit and the battery.
However, in case where an element having a parasitic diode such as a p-channel MOS transistor (hereinafter referred to as “pMOS transistor”) is used as the backflow prevention means, a voltage applied to the battery may be increased by the parasitic diode. Therefore, a voltage exceeding a rated value may be applied to a battery when the voltage of the battery becomes close to the full-charge voltage. When a voltage exceeding a rated value is applied to a lithium battery or the like, which is currently mainstream, the battery may ignite in the worst case.